Readiness Scores: What They Really Measure

Every ring and watch now hands out a morning number with a name like readiness or recovery. It is colored green, yellow or red and quietly suggests how hard the day should be. The number is worth understanding, because it is not a measurement. It is an opinion built from measurements.

What goes into it

Overnight the device records real signals. Heart rate variability, how much the spacing between heartbeats changes from beat to beat. Resting heart rate. Skin temperature. Breathing rate. How long you slept and how often you woke. Each is compared with your own baseline from the last few weeks. HRV below baseline, heart rate above it, temperature up and sleep short all point the same direction, and the device weights them, on some brands adds your recent activity, and prints a score. The weights differ by brand and are not published.

That design explains what the score does well. Alcohol, a cold on its way in, a stretch of short nights or a week of hard training push every input the same way at once. The score drops, and it usually agrees with how you feel.

Where it misses

The score cannot tell planned stress from unplanned stress. A hard interval session or a heavy squat day drops the next morning's number, and that is exactly the stress the plan called for. A device that colors the morning after yellow is reading the load, not judging whether it was a mistake.

HRV swings a good deal from one night to the next in a healthy person with nothing wrong, so one low morning is as likely to be noise as signal. The menstrual cycle moves temperature and HRV in a predictable pattern, so many women see a lower score in the second half of the cycle that is normal physiology.

And a high score does not mean the body is primed for a personal best. It means nothing was wrong overnight, which is a different claim.

How to use it

Read the trend, not the day. A seven day average sitting below your thirty day baseline is worth acting on. One red morning is not. If the score is low and you feel fine, train, perhaps a notch easier. If it is low two or three mornings in a row, take an easy day. In small trials, training adjusted by HRV did about as well as a fixed plan, sometimes slightly better. The signal helps at the margin. It should not run the program.

The most useful habit is to open the components rather than the headline. Resting heart rate up three beats and temperature up half a degree often looks like a cold on its way in. HRV down with everything else normal the morning after a 10 mile run is the run. The score blurs the two. The parts tell them apart.

We read members' overnight data alongside their training plan, labs and VO2 test, because the pattern over weeks carries the information.

This article is educational and is not medical advice.

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